The present invention relates to an optical data reading device for reading data from a disk type recorded data carrier.
FIG. 1 is a side elevational view of a prior art device where a disk 1 has no warp and a spacing A between the disk 1 and an optical pick-up head 3 is kept constant. The disk 1 is rotated by a motor-driven spindle 2.
The optical pick-up head 3 is held close to the underside of the disk 1 by a transfer base 4 and is pivotable on the base 4 about a shaft 5.
The transfer base 4 can be moved to and fro in the radial direction of the disk 1 along a guide rail 6 by a transfer mechanism (not shown), thereby forming a feed mechanism.
The optical pick-up head 3 is provided with an objective lens 7, and the disk 1 is irradiated with a light flux 8 which is focused through the objective lens 7, in order to read data stored on the disk.
In FIG. 2, the disk 1 is shown warped and as a result the spacing between the disk 1 and optical pick-up head 3 changes to B. The disk 1 is warped upward, and the optical pick-up head 3 is pivoted around the shaft 5 so that the head is maintained substantially parallel to the adjacent part of the disk.
However, although the pick-up head 3 may follow the tilting component of warp of the disk 1, it cannot follow the component of vertical displacement of the disk 1. Therefore, it is necessary to use fully the function of an automatic focusing device in the optical pick-up head 3 such as the objective lens 7. As a result, the automatic focusing device must have a tracking range large enough to compensate for maximum warp of the disk 1. This may not always be convenient.
Thus, the spacing A between the disk 1 and the optical pick-up head 3 in the example of FIG. 1 changes to B in FIG. 2 and the distance (B-A) may not be fully compensated.